First gaseous sulfuric acid measurements in automobile exhaust: Implications for volatile nanoparticle formation

Gaseous sulfuric acid (GSA) is thought to represent an important if not the most important nucleating gas present in modern diesel automobile exhaust. It triggers the formation of new aerosol particles, which grow by condensation and coagulation. Here we report on the first measurements of GSA in automobile exhaust. The experiment was made using a modern passenger diesel car equipped with an exhaust after-treatment system composed of an oxidation catalyst and a diesel-particle filter. The diesel fuel used had an ultra-low sulfur mass fraction of only 5×10−6. Measured GSA number concentrations reached up to 1×109 cm−3. Freshly nucleated particles with diameters larger than 3 nm were also measured. The concentrations reached up to 1×105 cm−3 and were positively correlated with GSA for GSA exceeding a threshold value in the range of 5×107–2×108 cm−3. This suggests that GSA was involved in the formation of new volatile particles.